To improve the printing properties of a recording medium, a coating composition is sometimes applied to its surface to form a coating thereon. For example, a coating can impart a superior feel and a photograph-like quality to a printed image; a highly absorptive coating can reduce the smearing and rub off of an image, and a coating that immobilizes (i.e., adsorbs) colorants at the outer surface of the coating can enhance the waterfastness, sharpness, resolution and color density of a printed image.
Coating compositions as described above can be applied to various types of recording media, including those used in ink jet and laser printing processes. In a typical ink jet printing process, a print head scans the recording medium in horizontal strips, using a motor assembly to move it from left to right, as another motor assembly rolls the recording medium vertically through the ink jet printer. As the recording medium is fed vertically through the ink jet printer, ink is emitted from nozzles in vertical rows of pixels to eventually form an image. This differs from, for example, a laser printing process where an image is printed (or copied) onto a recording medium by depositing a uniform electric charge on a photoconductor drum in the dark; exposing the drum to a pattern of light, thereby creating a latent image area; developing the pattern by adding toner particles to the latent image area; transferring toner particles to the recording medium as it is passed over the drum; fusing the toner particles to the recording medium by applying heat and pressure thereto; and cleaning the photoconductor drum.
There are several advantages of using an ink jet printing process as compared to a laser printing (or copying) process. Indeed, ink jet printing can be done with less expensive hardware and can be used with a variety of different substrates. As a result, the demand for improved ink jet recording media has grown, particularly recording media exhibiting the characteristics described above.
It is a challenge, however, to prepare an ink jet recording medium having a coating that is at once glossy, absorptive, and immobilizing. Gloss and colorant immobilization can sometimes be achieved by incorporating different types of polymeric resins into a coating composition. For example, gelatin, polyvinyl pyrrolidone and/or polyvinyl alcohol can be used to produce glossiness, while a cationic polymer resin can be used to promote the surface immobilization of an anionic colorant. However, inks applied to polymer-coated ink jet recording media dry relatively slowly, and often have an undesirable tendency to smear and rub off. While some substances such as certain treated kaolin clays or treated calcium carbonates can immobilize colorants, the overall absorptivity and rate of absorption are sometimes compromised with such substances.
Thus, a need remains for an ink jet recording medium having a coating that is at once glossy, absorptive, and immobilizing. The present invention seeks to provide such a recording medium. These and other advantages of the invention will be apparent from the description of the invention provided herein.